About 10,000 people fled the Somali capital in the last week alone, and the exodus sparked by fighting continues, the United Nations said Monday.
The United Nations High Commissioner for Refugees said even those who had returned to Mogadishu recently are heading out again, fearing for their safety.
"The prospect of still another round of heavy fighting has set many civilians on the road once more," the agency said in a statement.
Mogadishu has seen little peace since government troops backed by Ethiopian forces drove an Islamic movement out of the city in December. Roadside bombs, attacks on government installations, assassination attempts and gunbattles have become common, and civilians are often caught in the crossfire.